1. Field of the Invention
This invention relates to a method for production of an air-tight, heat-resistant plate suitable for use in manufacturing bulbous fluorescent lamps, in particular. More specifically, it is concerned with provision of air-tight, heat-resistant plate for fixedly securing, with good air-tightness, in the production of the above-mentioned bulbous fluorescent lamps, stems for holding thereon the electrodes, a fluorescent inner tube (a tube coated on its inner surface with a layer of light emitting substance), or an outer glass tube for protecting the fluorescent inner tube, a gas discharge tube, and so forth.
2. Discussion of Background
The following are the major characteristics required, in general, of such air-tight, heat-resistant plate:
(i) its thermal expansion coefficient is coincident with that of the fluorescent inner tube, the gas discharge tube or the outer glass tube, which is approximately 9.0 to 10.5.times.10.sup.-6 /.degree. C. (an average thermal expansion coefficient at a temperature range of from 25.degree. C. to 500.degree. C.);
(ii) it maintains such high air-tightness that does not permit leakage of a gas sealed therein;
(iii) it has excellent adhesiveness and air-tightness with a low melting point glass for sealing; and
(vi) it is durable against usual sealing temperature of from 400.degree. C. to 500.degree. C.
In recent years, fluorescent lamps have taken a variety of forms, and, as one of such forms, bulbous fluorescent lamps of different designs have been developed.
FIG. 1 of the accompanying drawing shows one example of such bulbous fluorescent lamp, in which the fluorescent inner tube 2, the outer glass tube 3, the stems 4 for holding the electrodes, the gas discharge tube 5, and so on are assembled on a single sheet of the air-tight, heat-resistant plate 1 and sealed with a low melting point glass 6.
The material which consists essentially of an inorganic filler and glass powder (i.e., a glass-ceramic type material), and which is usually used for the production of such air-tight, heat-resistant plate has been well recognized among those in this field of technology owing to its advantageously low cost, its excellent shapability into product of various configurations, and other characteristics. In spite of such remarkable characteristics, however, there has so far been found no air-tight, heat-resistant plate which meets all the requirements of the thermal expansion coefficient, air-tightness, electric insulation, heat-resistance, and other properties for particular use in the manufacture of the above-mentioned bulbous fluorescent lamps.
In view of such situation, there has been strong demand for emergence of the glass-ceramic type material satisfying all the characteristic requirements as mentioned above adapted for the production of the air-tight, heat-resistant plate for the bulbous fluorescent lamps.